The present invention relates to a system for detecting linear dimensions of a workpiece, including a checking probe with detecting devices, a power supply connected to the checking probe, a remote transceiver unit, integral with the probe, connected to the detecting devices and to the power supply, and adapted for wireless transmitting signals indicative of the state of the probe, and a stationary transceiver unit, adapted for wireless transmitting activation signals to the formerly mentioned remote unit, wherein the remote transceiver unit includes receiving devices adapted for receiving the wireless transmitted signals, a processing section, connected to the receiving devices, and to the power supply and adapted for generating an enable signal, the processing section including at least an amplifier connected to the receiving devices for outputting an amplified signal, a switching unit connected to the processing section and to the power supply, and additional sections, with generating and transmitting circuits, connected to the switching unit, the switching unit being adapted for receiving the enable signal and, on the basis of this signal, controlling the power supply of at least some of the additional sections.
There are known measuring systems as, e.g. systems in numerical control machine tools, for detecting the position and/or the dimensions of machined workpieces by a contact detecting probe, mounted in the machine, that, in the course of a checking cycle, displaces with respect to the workpiece, touches the surfaces to be checked and responds to contact by wireless transmitting signals to a receiving unit, usually located at a certain distance from the probe.
The receiving unit is in turn connected, by means of an interface device, to the numerical control unit that, by processing other signals indicative of the spatial position of the probe, provides information about the position of the workpiece surfaces.
The contact detecting probe can include electric batteries for the power supply of contact detecting circuits and the wireless transmission devices. The wireless transmission can take place, for example, by emitting electromagnetic signals of optical or radio-frequency type. Since the probe is utilized just for short time intervals during the machining cycle of the machine tool, the associated detecting circuits and transmission devices are normally kept in a xe2x80x9cstand-byxe2x80x9d state of low power consumption and powered-up only when there is the need to perform a checking cycle. The switching from the xe2x80x9cstand-byxe2x80x9d state to the full xe2x80x9cpowered-upxe2x80x9d state can be accomplished by controlling suitable switching devices on the probe by means of activation signals wireless transmitted by the receiving unit. When the measuring cycle ends, the probe circuits return to the xe2x80x9cstand-byxe2x80x9d state of low power consumption either by wireless transmitting a suitable deactivation signal, or, as an alternative, after a predetermined time period has elapsed.
U.S. Pat. No. 4,779,319 discloses a measuring system with these characteristics and more specifically it describes a checking probe with circuits for transmitting optical signals in the infrared band. An infrared radiation flash is utilized for activating the probe, in other words for controlling the full power-up of the probe detecting circuits and the transmission devices.
The probe circuits for receiving the optical activation signal and controlling the connection to the batteries include a receiver diode and a coil that, among other things, serves as a high pass filter for reducing the negative effects due to the steady state and/or low frequency components of the environment illumination and for excluding from subsequent processings low frequency pulses emitted, for example, by fluorescent lamps located in the probe environment.
However, it may occur that the fluorescent lamps, or other sources of light, emit electromagnetic radiations with frequencies in the same band as the activation or deactivation signals (or, more specifically, the associated modulating signals) and that these radiations cause the unwanted activation of at least some of the probe circuits, and a useless consumption of the battery supply energy, or the unwanted deactivation in the course of a checking cycle and imaginable negative consequences.
A fluorescent lamp can emit improper and unforeseeable radiations, even in the infrared radiation band, that vary depending on the type of lamp, on the environment temperature, on the power supply voltage, on the age and the efficiency conditions of the lamp itself.
Another possible way for probe optical activation (or deactivation) foresees, as an alternative to the pulse signal described in patent U.S. Pat. No. 4,779,319, an infrared radiation signal modulated as a sequence of pulses of a given frequency (for example, about ten KHz) and transmitted to the receiving unit for a determined time period (for example, a few tenths of a second). The probe circuits include a logic sectionxe2x80x94that is powered when there is detected a signal of sufficient intensityxe2x80x94that checks whether the received signal has the required frequency and minimum duration (a number of pulses generally by far smaller than those actually transmitted) of the activation (or deactivation) signal and that, in the affirmative, causes the power-up of the other probe circuits (or the return to the stand-by state).
The intensity of the radiations randomly emitted by the fluorescent lamps in the frequency band of the activation signal can be sufficient for causing the frequent and needless power-up of the logic section of the probe circuits, and consequently unwanted consumption of the battery energy. Furthermore, while the logic section is improperly powered, it may occur that a sequence of pulses be sent by a fluorescent lamp whose frequency and duration are the same as those of the activation signal. It may also occur that, while the probe is performing a checking cycle, the logic section detects a sequence of pulses having frequency and duration that match those of the deactivation signal, without the latter signal having actually been transmitted by the receiving unit.
Object of the present invention is to overcome the inconveniences, in terms of consumption of the battery supply energy and undesired probe activation or deactivation, caused by fluorescent lamps, or by other sources emitting electromagnetic radiations in the probe environment.
This and other objects are achieved by a system in which the processing section of the remote transceiver unit includes attenuation devices adapted for inhibiting the generating of the enable signal on the basis of attributes of the signal that the receiving devices have wireless received, the attenuation devices including elements of a feedback circuit for attenuating the intensity of said amplified signal.